DISCLAIMER - everybody's eyes are different. That said...
Agreed with others - flicker-free is a BIG deal (well, for me, at least), and, I've over the past few years tended to use the "warm" preset. May not be perfect in terms of colors, but, for me, it's easier on the eyes than some of the really bright whites that seem to almost have a bluish tinge.
snurp85 :
Aside from that, most any brand is fine (asus, acer, etc). I would suggest that if you are getting something that is only 1080p, dont go too large (>28") or you will start to see individual pixels, which might be a negative.
I'm actually relieved to see someone besides myself who considers even 27 and 28 inch monitors at 1080p acceptable. A lot of people tend to put 23-24 as the max for 1080p, but I was always very comfortable with 1080p on a 27-inch.
I might've even considered up to 30" or so at 1080p - when I run 1080p on a 27" monitor, I find myself indecisive between running Windows at normal size, or with things scaled up to 125%. The latter seems slightly too big, and slightly out of focus, but at 100%, seems sharp, but slightly too small.
(again, disclaimer, my particular eyeballs)
I am normally comfortable buying things online, but with monitors, going to stores that have a lot on display, and actually trying them out seated in front of them is a big deal. I
highly recommend having her try out a few in-person if at all possible.
Also - if for work - does work typically, say, have a dual-1080p monitor setup? Where I work does. Situations like this might make a 3440x1440 or even those new 3840x1600 ($expensive$) monitors worthwhile, to have the space needed that you would typically have with two side by side monitors. I think Samsung has even just released a huge 3840x1080 monitor. I don't know if 32:9 aspect ratio is going to be comfortable or not, but, it might be worth considering, depending on what your girlfriend's normal work setup is like.